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WRC BUL 484

2003 Edition, July 1, 2003

Complete Document

GASKETED JOINT EMISSIONS AND LEAKAGE



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Product Details:

  • Revision: 2003 Edition, July 1, 2003
  • Published Date: July 2003
  • Status: Active, Most Current
  • Document Language: English
  • Published By: Welding Research Council (WRC)
  • Page Count: 38
  • ANSI Approved: No
  • DoD Adopted: No

Description / Abstract:

Part-1 - These projects document the correlation of precise laboratory leak rate measurements with the EPA Method 21 protocol for PPMV (parts per million by volume) measurements with Helium and Methane using the standard bagging technique. An instrumented NPS 4 class 600 bolted joint fixture with a flexible graphite sheet gasket was used. Large to very low flow rates in Helium and Methane were investigated with the gasket subjected to a stress range of 1000 to 15000 psi (8.to 103 MPa) gasket stress and pressures from 50 to 800 psi (0.35 to 8.5Mpa). Concluding that the standard EPA bagging method is accurate for PPMV emission measurements, the authors also question sniffing around a flange in an open environment as a reliable method of emissions measurement. More important to plant engineers is confirming the reliability of EPA Method 21 flow formula as a means to compare field PPMV measurements with reported laboratory leakage results as an aid to gasket selection.

Part-2 - The effect of longer-term exposures under load at elevated temperature, such as in operating plants, begged several well-founded questions. For example, is there gradual but continuing creep-relaxation, or does leakage increase or decrease over time? Also, does degradation or hardening or other physical effects occur over time that affects emissions? In this project, at least for the two typical materials studied, the investigators found clear trends. The answer, surprising to some, is that the yearlong exposure had no significant adverse effect. Neither of the materials experienced meaningful creep, or thickness change, and both maintained an essentially steady leak rate.

Part-3 – Explores in a parametric format a number of questions about predecessor ATRS and ARLA gasket screening projects. Issues such as the effect on leakage of the contained media, high vs. low internal pressure, initial seating stress and joint rigidity were explored using the more precise and comprehensive HOTT (Hot Operating Tightness Test) in a versatile test rig capable of mimicking a variety of real joints. The HOTT test tracks real-time leakage and relaxation while simulating the rigidity of typical joints and the ATRS and ARLA test fixtures. Sheet graphite gaskets exposed to 800 psi (5.5 MPa) air and 950OF (510OC) were the base case as, pressure, rigidity, initial stress, fluid type and the presence of oxidation inhibitor were investigated to determine whether degradation and leakage were reduced or aggravated. Findings indicate that pressure, media and joint rigidity are the most significant on the degradation rate while initial gasket stress levels (below 8100 psi) and, surprisingly, the presence an oxidation inhibitor are much less significant. Effect. Additional testing performed under other initial loads and with air at lower pressures is recommended to confirm these observations. Importantly the investigation tells us that the simple ATRS/HATR test remains an acceptable screening indicator of gasket behavior and confirms the qualification protocols developed in PVRC Projects 91 8 and 93 3 for flexible graphite based sheet materials for a broad range of real world applications